IMMUNE SYSTEM MODULATION USING PSORALENS ACTIVATED WITH VISIBLE LIGHT

Abstract: Methods and pharmaceutical compositions for modifying the immune response of a mammal are provided. The pharmaceutical compositions include a pharmaceutically acceptable carrier and a plurality of cells containing psoralen-DNA monoadducts and substantially no psoralen-DNA crosslinks. The preparation is formed by irradiating a suspension of cells with visible light radiation in the presence of psoralen.

Description: IMMUNE SYSTEM MODULATION USING PSORALENS ACTIVATED WITH VISIBLE LIGHT Field of the Invention This invention relates to methods and pharmaceutical compositions for augmenting an immune response. The methods include irradiating cells with visible light in the presence of psoralen molecules. Background of the Invention The psoralens are a group of photoreactive compounds that are activated by radiation falling within a broad range of wavelengths. Photoactivation of a psoralen molecule yields a transient species which is capable of covalently binding to a cellular target molecule in a manner which severely interrupts cellular function. The transient species remains reactive for microseconds, long enough to be chemically reactive and short enough so that, for practical purposes, once the source of irradiation is turned off, the unbound psoralen reverts to its inert form. As a consequence of these unique characteristics, psoralens provide the clinician with a class of pharmacologic agents having high chemotherapeutic potency, but only where and when the psoralens come in contact with light of an appropriate wavelength (Edelson, R. , "Photopheresis: A Clinically Relevant Immunobiologic Response Modifier", Annals of N.Y. Academy of Sciences 636:154-164 (1991)). One of the most widely used psoralens, and the only psoralen currently approved for clinical use, is 8-methoxypsoralen (8-MOP). 8-MOP is a linear furocoumarin and has an absorption spectrum which shows substantial absorption of energy at wavelengths between about 200 nm and 320 nm, a precipitous drop in absorption at wavelengths between 320 and 400 nm and very little absorption at wavelengths greater than 400 nm (visible wavelengths) . In view of these well known absorption characteristics, psoralens historically have been activated by energy in the ultraviolet end of the energy spectrum. In the presence of ultraviolet A radiation (UVA, 320 nm - 400 nm) , 8-MOP is capable of reacting with a wide spectrum of target molecules, e.g., cellular DNA, to form a mixture of photoadducts. Recently, Gasparro, et al. , demonstrated that a form of DNA located on the cell surface, cell membrane DNA (CM-DNA), could be photomodified by 8-MOP in the presence of ultraviolet radiation (Gasparro, F. , et al., "Cell membrane DNA: a new target for psoralen photoadduct formation", Photochem. Photobiol . 5^:315-321 (1990). In a follow up study, Perez, et al. , demonstrated that 8-MOP photomodified CM-DNA appears to play a role in immunologically mediated events (Perez, M.I., et al. , "DNA associated with the cell membrane is involved in the inhibition of the skin rejection response induced by infusions of photodamaged alloreactive cells that mediate rejection of skin allograft", Photochem. Photobiol ■ 58:839-849 (1992). In addition, numerous studies have reported on the effects of 8-MOP and ultraviolet A radiation on amino acids and proteins, although no 8-MOP amino acid adduct has been fully characterized (Midden, W.R. , "Chemical mechanisms of the bioeffects of furocoumarins: the role of reactions with proteins, lipids, and other cellular constituents", Psoralen-DNA Photobiology (Edited by F.P. Gasparro), Vol. 11:1-19, CRC Press Boca Raton, FL (1988) and references therein; Schlavon, 0. and Veronese, F. , "Extensive crosslinking between subunits of oligo eric proteins induced by furocoumarins plus UV-A irradiation," Photochem. Photobiol . 43:243-246 (1986); Granger, M. and Helene, C, "Photoaddition of 8-methoxypεoralen to E. coli DNA polymerase 1. Role of psoralen photoadducts in the photosensitized alterations of pol 1", Photochem. Photobiol. 38:563-568 (1983); Megaw, J., et al., "NMR analyses of tryptophan-8-methoxypsoralen photoreaction products formed in the presence of oxygen", Photochem. Photobiol . 32: 265-269 (1990)). Midden, et al. and Caffieri, et al . have independently characterized psoralen lipid photoadducts. (Midden, W.R., Psoralen-DNA Photobiology, supra. ; Specht, K.G., et al. , "A new biological target of furocoumarins: photochemical formation of covalent adducts with unsaturated fatty acids," Photochem. Photobiol ■ 4J:537-541 (1989)) (Caffieri, S., et al. , "Formation of photoadducts between unsaturated fatty acids and furocoumarins", Med. Biol , Environ. lj>: 11-14 (1987)). However, only psoralen-DNA photoadducts have been fully characterized (Cimino, G.D., et al . , "Psoralens as photoactive probes of nucleic acid structure and function: organic chemistry, photochemistry, and biochemistry", Ann. Rev. Biochem. 5_4:1151-1193 (1985); Kanne, D., et al . , "Psoralen-deoxyribonucleic acid photoreaction. Characterization of the monoaddition products from 8-methoxypsoralen and 4,5' ,8-trimethylpsoralen" , Biochemistry 21:861-871 (1982); Teεsman, J.W., et al . , "Photochemistry of the furan-εide 8-methoxypsoralen-thymine monoadduct inside the DNA helix. Conversion to diadduct and to pyrone-side monoadduct", Biochemistry 2_4:1669-1676 (1985)) There are three principal types of psoralen-DNA photoadducts: furan ring-DNA monoadducts (4',5'-monoadducts or 4',5'-MA), pyrone (cou arin) ring-DNA monoadducts (3,4-monoadducts or 3,4-MA), and psoralen-DNA crosslinks. As used herein, the term monoadduct refers to a photoreaction product in which the reactive group of a target molecule, such as a pyrimidine base of DNA, is covalently coupled to either the furan ring or the pyrone ring of a psoralen molecule. The terms psoralen-crosslink or psoralen-diadduct refer to a photoreaction product in which the psoralen molecule is covalently coupled through both the furan ring and the pyrone ring to two different reactive groups of at least one target molecule, e.g., the crosslink is formed between two pyrimidine bases located on different strands of a DNA double helix. A diverse population of psoralen-DNA photoadducts is formed as a result of the sequential absorption of photons by psoralen and psoralen-monoadducts. Upon absorbing a first photon of ultraviolet A (UVA) , 8-MOP is activated to a transient species which forms a covalent bond to a reactive group of a target molecule, e.g., a pyrimidine base of a DNA, to form a psoralen-DNA monoadduct. Theoretically, either ring (furan or pyrone) may be activated with UVA radiation to form the psoralen-DNA monoadduct. Psoralen monoadducts represent a relatively small percentage (less than 50 %) of the total photoadducts formed upon activation of psoralen under photochemotherapeutic reaction conditions, such as those used in photopheresis (described below) . This is because the monoadducts are capable of absorbing a second photon of radiation to form a psoralen-DNA crosslink between reactive groups of the target. In general, when the target molecule is DNA, a psoralen crosslink is formed between pyrimidine bases located on two different strands of a DNA helix. As a result of crosslink formation, DNA replication is prevented. In effect, the psoralens extend the range of wavelengths than can be used to photochemically damage DNA from wavelengths less than about 310 nm (at which wavelengths DNA is subject to direct photochemical damage from the radiation) to the long-wavelength ultraviolet (UVA wavelengths, 320-400 nm) . The synthesis and characterization of the three principal psoralen-DNA photoadducts formed between HMT 4 '-(hydroxymethyl)-4,5 ' ,8-trimethylpsoralen (HMT, a synthetic derivative of 8-MOP) , and a low molecular weight synthetic oligonucleotide duplex have been described (Spielmann, H. et al . , "New Methods for the Large-Scale Synthesis of Furanside Psoralen Monoadducts and Diadducts", Photochem. Photobiol . 5_3:1135 (1991)). Spielmann, et al. report that reaction of a DNA 12mer (a DNA oligomer containing 12 bases) and a complementary DNA 8mer (8 bases) with HMT, in the presence of krypton laser irradiation at 406.7 nm, yielded 14% 12mer furan ring monoadducts and 10% 8mer furan ring monoadducts. Irradiation of the above-described oligomers and HMT in the presence of an argon ion laser (wavelength = 366 nm) yielded between 50-80% psoralen-DNA crosslinks (diadducts). In a related work, Sastry, et al . prepared the above-described photoadducts by reacting an excess amount of psoralen with oligonucleotide duplex, i.e., 1.6 x 10 —4 M HMT (48 ug/ml) to 0.4 x 10 —4M oligonucleotide duplex, in the presence of a krypton (406.7 nm or 413 nm) or argon (364 nm) laser (Sastry, S., et al. , "Recent advances in the synthesis and structure determination of site specific psoralen-modified DNA oligonucleotides" , J. Photochem. Photobiol . B: Biol. L4:65-79 (1992)). Sastry, et al . report that irradiation of the HMT/oligonucleotide reaction mixture at 406.7 nm yielded a mixture of furan ring-oligonucleotide monoadducts and unmodified oligonucleotides. Pyrone ring monoadducts were not detected when the krypton laser was used to synthesize monoadducts at the longer wavelength. Irradiation of the oligonucleotide duplex in the presence of HMT at 364 nm with an argon laser yielded an HMT-oligonucleotide duplex crosslink. Pyrone ring-oligonucleotide monoadducts were produced from the HMT-crosslink by reversing the furan ring-duplex bond under basic conditions. It is not clear whether the photoadducts observed by Sastry, et al . would in fact be formed under typical photochemotherapeutic conditions, e.g., irradiation of a heterogeneous preparation of cells in the presence of a substantially lower psoralen concentration (1 ug/ml). 8-MOP is significantly less soluble than HMT and cannot be obtained in solution at the concentration used by Sastry, et al . Moreover, unlike conventional photopheresis, the Sastry, et al . photochemical reaction contained a homogeneous population of target molecules in the absence of o ' ther potentially interfering cellular components. In view of the multitude of potential reactions between psoralen and the array of olecules present in a photophereεis cell preparation ("T Cell Molecular Targets for Pεoralenε", Annals of N.Y. Academy of Science 636:196-208 (1991), Malane, M. and Gasparro, F.), it is unlikely that the photoadducts described by Saεtry, et al . would be formed under typical photochemotherapeutic conditionε. Although long wavelength ultraviolet radiation (UVA, 320-400 nm) and 8-methoxypεoralen (8-MOP) iε an eεtabliεhed photochemotherapy for treating diεorders of the immune system, the molecular basis for the therapeutic effect of psoralen photochemotherapy has not been elucidated. Formation of psoralen-DNA photoadducts (monoadducts and crosslinks) has been presumed to be responεible for the efficacy of theεe therapieε. The therapeutic effectε of psoralen photochemiεtry may be dependent upon the claεε of adduct formed aε well as upon the DNA context of the adduct (Averbeck, D., "Mutagenesis by psoralenε on eukaryotic cells", Photoεensitization, ed. G. Moreno NATO ASI Series Ij5:279-291 (1988); Averbeck, D., "Recent advances in psoralen phototoxicity mechanism", Photochem. Photobiol . 50 :859-882 (1989); Sage, E., and Bredberg, A., "Damage distribution and mutation spectrum: the case of 8-methoxypεoralen pluε UVA in mammalian cells", Mutation Research 2_6_3:217-222 (1991)); Cundari, E., Averbeck, D. , "8-Methoxypεoralen- photoinduced DNA croεslinkε aε determined in yeast by alkaline step elution under different reirradiation conditionε. Relation with genetic effectε", Photochem. Photobiol. 48:315-320 (1988); Bredberg, A. and Nachmanεεon, N. , "Psoralen adducts in a shuttle vector plasmid propagated in primate cells: High mutagenicity of DNA crosε-links, " Carcinogenesiε 8:1923-1927 (1987); Averbeck, D., et al. , "Mutagenic and recombinogenic action of DNA monoadducts photoinduced by the bifunctional furocoumarin 8-Methoxypsoralen in yeast (Saccharomyces cereviεiae)" , Photochem. Photobiol . 45 :371-379 (1987); Cassier, C, et al . , "Mutagenic and recombinogenic effectε of DNA cross-links induced in yeast by 8-methoxypεoralen photoaddition" , Photochem. Photobiol . 3^:799-803 (1984)), Shinghal, R.P., et al . , "High-performance liquid chromatography for trace analyεis of DNA and kinetics of CNA modification", BioChrom. ^ :78-88 (1989); Sage, E., and Moustacchi, E., "Sequence context effectε on 8-methoxypεoralen photobinding to defined DNA fragments", Biochemistry 26:3307-3314 (1987)). The ability of a cell line to repair lesionε alεo affectε the toxicity and mutagenicity of psoralen-DNA photoadducts (Potapenko, A.Y. , "Mechanisms of photodynamic effects of furocoumarins", J. Photochem. Photobiol . B. 9:1-33 (1991); Babudri, N. , et al. , "Mutation Induction and killing of V79 Chinese hamster cells by 8-methoxypsoralen plus near-ultraviolet light: relative effects of monoadducts and crosεlinkε", Mutation Reε . 9_l:391-394 (1981)). Accordingly, cellular mutationε may arise as a consequence of misrepair or miεreading during mitoεiε of the psoralen-DNA lesion. Indirect evidence suggests that the psoralen-DNA crosslink may be the most mutagenic of the psoralen-DNA lesions (Averbeck, D., Photosenεitization, NATO ASI Series 15:279-291 (1988) supra; Cundari, E., Averbeck, D., Photochem. Photobiol . 4_8:315-320 (1988) supra; Bredberg, A. and Nachmansson, N., Carcinogenesiε 8:1923-1927 (1987) supra; Sage, E., Bredberg, A., Mutation Research 263:217-222 (1991) supra; Cassier, C. , et al . , Photochem. Photobiol . 39 :799-803 (1984) εupra) . Pεoralen photochemotherapy haε been shown to alter cellular antigenicity (Malane, M. , et al. , "Treatment with 8-methoxypsoralen (8-MOP) and ultraviolet A (UVA) radiation enhanceε immune recognition in a murine maεtocytoma model", J. Inveεt. Dermatol ■ 9_8:554A (1992)). It is believed that psoralen photoadduct formation modulateε the immune system response by causing cellular mutations which result in phenotypic cellular changes. Accordingly, psoralen photochemotherapy has been directed to (1) regulating an aberrant immune system response via modification of the T cell εurface receptor, e.g., by inducing presentment of a novel T cell receptor or (2) augmenting the immune εyεtem response to a specific antigen, e.g., by inducing presentment of novel antigenic peptideε aεεociated with major hiεtocompatibility complex moleculeε on the cell εurface. Several εtudieε, deεcribed herein, have suggeεted that the ability of the immune εyεtem to recognize the receptor of an aberrant T cell clone as antigenic makes possible the vaccination of a patient against a pathogenic clone of T cells, i.e., by administering to the patient photochemically modified aberrant T cells. Cutaneous T cell lymphoma (CTCL) is an example of an immune syεtem diεeaεe that iε cauεed by a maεεive expansion of a εingle clone of aberrant T cells. Extracorporeal photochemotherapy ("photopheresiε") for the treatment of cutaneous T cell lymphoma has been described (Edelεon, R. , "Light-activated Drugε", Scientific American 256(8) : 68-75 (1988); Edelεon, R. , Annalε of N.Y. Academy of Scienceε 636: 154-164 (1991) εupra. The treatment compriεeε iεolating the patient's T cells, irradiating the cells with ultraviolet A radiation in the presence of a photoactivatable agent, e.g., 8-MOP, and reinfusing the damaged T cells. This therapy reportedly reεultε in εelective deεtruction of the malignant T cell clone. Conventional photopheresis (irradiation with ultraviolet A radiation in the presence of 8-MOP) has also been used for the treatment of εeveral autoimmune diεσrderε, including pemphigus vulgaris and εyεtemic sclerosiε (Rook, A., "Photopheresis in the Treatment of Autoimmune Diseaεe: Experience with Pemphiguε Vulgaris and Systemic Sclerosiε", Annals of N.Y. Academy of Science 636:209-216 (1991) and rheumatoid arthritis (Malawista, S., et al. , "Photopheresis for Rheumatoid Arthritis", Annals of N.Y. Academy of Science 636:217-226 (1991). Long wavelength ultraviolet radiation and 8-MOP have also been used aε a photochemotherapy for the treatment of psoriasis (Parrish, J., et al., "Photochemotherapy of psoriasis with oral methoxsalen and long wavelength ultraviolet light", N. Engl . J. Med. 29: 1207-1211 (1974)) and in a preliminary study to evaluate the potential therapeutic value of photopheresis in seven patients with AIDS-related complex (ARC) (Bisaccia, E. et al. , "Viral-Specific Immunization in AIDS-Related Complex by Photopheresiε", Annalε of N.Y. Academy of Science 636:321-330 (1991) . Photophereεis also haε been used prophylactically to prevent graft rejection by injecting into mice a preparation containing Photoinactivated Effector T ("PET") cells (Perez, M. et al . , "Inhibition of Antiskin Allograft Immunity Induced by Infusions with Photoinactivated Effector T Lymphocytes (PET Cells); "The Congenic Model", Transplantation 5JL: 1283-1289 (1991). To prepare the PET cells, T cell clones mediating skin graft rejection were expanded in vivo and photoinactivated by ultraviolet irradiation in the presence of 8-MOP. Perez, et al . report that thiε procedure results in the adoptive transfer of tolerance for skin allotransplantation, as demonstrated by prolongation of allograft survival in the recipients of PET cells. The above-deεcribed photophereεis procedures have also been used to augment the immune syεtem response to a specific antigen. In particular, U.S. Pat. No. 4,838,852, issued to Edelεon et al . (hereinafter Edelεon '852), the contentε of which are incorporated herein by reference, describeε a method for enhancing the immune εyεtem response of a mammal to an antigen. The Edelson '852 method comprises (a) contacting the subject's immune system with the specific antigen for a suitable time to artificially stimulate the immune system, (b) withdrawing antigen-stimulated blood cell material from the subject, (c) treating the withdrawn material to alter the antigen-stimulated cells, and (d) returning the treated material to the subject. Edelson '852 alεo diεcloseε that it may be possible to render the cells incapable of recognizing an antigen by withdrawing the blood cell-containing material from the εubject, treating the withdrawn material as above, returning the treated material to the subject and then contacting the subject's immune syεtem with a specific antigen. U.S. patent no. 5,147,289, isεued to Edelson (hereinafter Edelson '289), the contents of which are incorporated herein by reference, describeε methodε for non-specifically enhancing the immune syεtem reεponεe of a mammal to an antigen. The method compriεeε (A) enhancing the immune system responεe by (a) withdrawing leukocyte containing material from the mammal, (b) treating the withdrawn leukccyteε in a manner to alter the cells, (c) returning the treated leukocytes to the mammal and (B) artificially contacting the mammal's immune system with the antigen for a suitable period of time to stimulate an immune syεtem response. With respect to the Edelson '852 and '289 patents, the withdrawn leukocytes may be altered by, for example, irradiating the leukocytes with ultraviolet radiation in the presence of a photoactivatable agent, e.g., a psoralen, exposure to ultraviolet light in the absence of a photoactivatable agent, and exposure to visible light in the presence of a photoactivatable agent such as hematoporphyrin. In a preferred embodiment, the leukocytes are gently damaged by ultraviolet radiation in the presence of a pεoralen. The combination of ultraviolet radiation (320-400 nm) and 8-MOP haε alεo been propoεed aε a photochemotherapeutic method for preventing reεtenoεis in a subject undergoing vascular recanalization (U.S. Pat. No. 5,116,864, issued to March et al . ) . Ultraviolet radiation in the range of about 320 to about 400 nm was discloεed to activate the pεoralen at the region of the recanalization. More recently, L. Deckelbaum, et al . deεcribed a method for preventing reεtenoεiε, which method includeε activation of 8-MOP with visible light irradiation to inhibit smooth muscle cell pr )liferation (Deckelbaum, L. et al . , "Inhibition of Smooth Muscle Cell Proliferation by 8-Methoxypsoralen Photoactivated by Visible Light", American Heart Assoc. 65th Scientific Session, abstract no. 135231 (1992)). Bovine aortic smooth muscle cells were exposed to 1 ug/ml 8-MOP and irradiated with a broadband blue light source (peak wavelength = 420 nm, bandwidth = 34 nm) . The formation of 8-MOP-DNA adducts in smooth muscle cells was confirmed by HPLC analysis. None of the above-cited references and patents disclose a method for modulating an immune system response, which method comprises administering a cell suspension containing a plurality of non-lethal psoralen-photoadductε (monoadductε) and εubεtantially no lethal pεoralen-photoadducts (crosslinks). Accordingly, there is still a need for psoralen photoactivation methods which permit formation of photochemically modified cellε containing psoralen-DNA monoadducts under conditionε which generate virtually no pεoralen-DNA croεεlinks. The photoactivation method would be leεs toxic to the irradiated cellε in compariεon with photopheresiε conditionε currently employed. SUMMARY OF THE INVENTION The preεent invention provideε methodε for forming a εuεpension of cells containing cellular nucleic acid-pεoralen monoadductε and pharmacological compositions containing the same. The cell suspension is administered to a mammal to modulate the mammal's immune syεtem response. According to one aspect of the invention, a method for forming a suεpenεion of cellε containing cellular nucleic acid-psoralen monoadductε iε provided. The method compriεes contacting a εuεpenεion of cells containing cellular nucleic acid moleculeε with a plurality of psoralen molecules to form a psoralen-cell εuεpenεion and extracorporeally irradiating the psoralen-cell suεpenεion with viεible light to form a plurality of cellular nucleic acid-pεoralen monoadducts. The use of visible wavelength radiation (400 nm to 700 nm) reεultε in a cell εuεpenεion which is subεtantially free of cellular nucleic acid-pεoralen croεεlinks. The radiation used for photoactivation of the psoralen is in a wavelength range greater than about 400 nanometers and iε preferably in a wavelength range equal to or greater than about 420 nanometers. A laser may be used to deliver high intensity radiation at the preferred visible wavelengths. In a preferred embodiment, a helium/cadmium continuous wave laser having a wavelength of 442 nanometers is used for psoralen photoactivation. A dosage in the range of about 10 to 40 2 J/cm is preferred. Alternatively, a continuous wave or low power pulsed light source can be used to practice the present invention. Other εuitable light sources include a mode-locked argon laεer and diode laεerε. The εuεpension of cells may be an isolate from a source that iε selected from the group consiεting of blood, lymph fluid, bone marrow, lymphatic organ tiεεue and tiεεue culture. In a preferred embodiment, the cellε are leukocyteε, the cellular nucleic acid iε DNA and the psoralen is selected from the group consisting of 8-methoxypsoralen, amino-methyltrimethylpsoralen, 5-methoxypsoralen and trimethylpεoralen. Most preferably, the cellε are T cells and the psoralen is 8-methoxypsoralen. According to another aεpect of the invention, a method for making a pharmaceutical preparation for adminiεtration to a mammal iε provided. The method compriεeε placing the above-deεcribed irradiated pεoralen-cell εuspenεion, or components of same, in a pharmaceutically acceptable carrier. According to yet another aεpect of the invention, a method for modifying the immune εystem responεe of a mammal is provided. The method compriseε adminiεtering the above-deεcribed pharmaceutical preparation to the mammal, preferably to a human. In a preferred embodiment, the pharmaceutical preparation iε εtored in aiiquots containing an amount of cellε with cellular nucleic acid-pεoralen monoadductε sufficient to odify the immune responεe of the patient. Selection of an amount of cellε neceεεary to augment the patient's immune responεe iε within the capabilities of those skilled in the art without the need for undue experimentation. The amount of cells is, in part, dependent upon the patient's age, weight and medical profile. Preferably, an amount of cells ranging from a minimum of about 25,000 to a maximum of about 200 x 10 antigen presenting cellε iε sufficient to augment the immune responεe of the patient (Ben-Nun, A., et al . , "Vaccination against autoimmune encephalomyelitis with T lymphocyte line cells reactive against myelin baεic protein", Nature 292:60-61 (1981); Holoshitz, J., et al. , "Lines of T lymphocytes induce or vaccinate againεt autoimmune arthritis", Science 219:56-58 (1983); Lider, O., et al. , "Anti-idiotypic network induced by T cell vaccination against experimental autoimmune encephalomyelitis", Science 239:181-183 (1988); Khavari, P., et al . , "Specific vaccination against photoinactivated cloned T cells", Abεtract Clin. Res . 3_6:662A (1988); and Edelson, R. , et al . "Treatment of cutaneous T cell lymphoma by extracorporeal photochemotherapy", N. Engl. J. Med. 316:297-303 (1987). According to yet another aεpect of the invention, a method for modifying the immune system responεe of a mammal to an antigen is provided. The method comprises withdrawing a suspension of cells containing nucleic acid molecules from the mammal, contacting the cells with a plurality of psoralen molecules to form a pεoralen-cell suspension; extracorporeally irradiating the pεoralen-cell suspension with visible light to form a plurality of cellular nucleic acid-pεoralen monoadducts; administering the irradiated psoralen-cell suspension to the mammal and artificially contacting the mammal's immune syεtem with the antigen for a suitable period of time to stimulate the immune system. The irradiated cell suspenεion contains a plurality of cellular nucleic acid-pεoralen monoadductε and εubεtantially no psoralen-nucleic acid crosslinks. In a preferred embodiment, psoralen is administered orally to the patient prior to withdrawing the suspension of cellε from the mammal. The antigen iε selected from the group conεiεting of peptideε, nucleic acidε, polyεaccharideε and analogueε thereof. In a preferred embodiment, the antigen iε an autologous antigen, or is asεociated with a variety of diseases and/or conditions including a solid tumor malignancy, an immunodeficiency diseaεe or a hyperεenεitivity disease. Such antigens are known to those of ordinary skill in the art. According to εtill another aεpect of the invention, a pharmaceutical compoεition for modifying an immune system response is provided. The composition compriseε a pharmaceutically acceptable carrier and a preparation of cellε, the cellε containing a plurality of cellular nucleic acid-pεoralen monoadductε and substantially no cellular nucleic acid-psoralen crosslinks. In a preferred embodiment, the ratio of cellular nucleic acid-psoralen monoadducts to nucleic acid-psoralen crosslinks is at least about 2 to 1, more preferably 10 to 1 and moεt preferably, 49 to 1. The cell εuεpenεion of the instant invention has a substantially higher proportion of psoralen-DNA monoadductε in compariεon with cells that have been photochemically altered according to conventional photopheresiε methods, e.g., irradiation with long wavelength ultraviolet radiation in the presence of 8-MOP. From indirect evidence, it has been inferred that the preferential formation of psoralen-monoadducts over crosεlinks results in fewer lethal cell mutations. Accordingly, the pharmacological preparation of the instant invention differs from that resulting from conventional photopheresis in containing a greater number of photochemically altered, viable cells. These and other aspectε of the invention as well as various advantages and utilities will be more apparent with reference to the detailed description of the preferred embodiments and in the accompanying drawings. Brief Description of the Drawings Figure 1 illustrates the structure of 8-methoxypsoralen (8-MOP); Figure 2 illuεtrates the absorption εpectrum of 8-methoxypεoralen; Figure 3 illuεtrates the effect of 419 nm light (VIS) and ultraviolet A (UVA) radiation on 8-methoxypsoralen degradation; Figure 4 schematically illustrates formation of an 8-MOP-DNA monoadduct upon absorption of a first photon of energy; Figure 5 schematically illuεtrateε formation of an 8-MOP-DNA croεεlink upon abεorption of a second photon of energy by the 8-MOP-DNA monoadduct of figure 4; Figure 6 illuεtrates the spectral output of the 419 nm lampε used to irradiate a pεoralen-cell suspenεion; Figure 7 illuεtrateε HPLC analyεiε of enzymatically hydrolyzed DNA from εmooth muεcle cells; and Figure 8 illustrates the spectral output of the 447 nm lamps used to irradiate a psoralen-cell εuεpension. Detailed Description of the Invention One method for forming a suspenεion of cellε containing cellular nucleic acid-pεoralen monoadductε compriεeε (a) contacting a εuεpenεion of cellε containing cellular nucleic acid with a plurality of psoralen molecules to form a psoralen-cell suεpension and (b) extracorporeally irradiating the psoralen-cell εuεpension with visible light to form a plurality of cellular nucleic acid-psoralen monoadducts. Irradiation with visible light resultε in a cell suspenεion containing primarily cellular nucleic acid-psoralen monoadducts and subεtantially no cellular nucleic acid crosslinkε. In general, the radiation used for photoactiva ion of the psoralen is in a wavelength range greater than about 40C nanometers and is preferably in a wavelength range equal to or greater than about 420 nanometers. A laser may be used to deliver high intensity radiation at the preferred visible wavelengths. In a preferred embodiment, a helium/cadmium continuous wave laεer having a wavelength of 442 nanometerε iε uεed for psoralen photoactivation. A dosage in the range of about 10 to 40 J/cm 2 is preferred. Alternatively, a continuous wave or low power pulsed light source can be uεed to practice the present invention. Other suitable light sources include a mode-locked argon laser and diode lasers. In a preferred embodiment, the visible light has a wavelength of about 450 nm and an intensity of about 6mW/cm 2. The psoralen-cell suspension is irradiated with visible light for about 1 to about 3 hours. The above-disclosed ranges are merely drawn to the preferred embodiments of the instant invention and are not intended to limit the scope of the invention to any particular combination of irradiation parameters. As would be apparent to one of ordinary skill in the art, and aε demonstrated in Exampleε 3 and 4 herein, the irradiation parameterε of wavelength, intenεity, time of irradiation are interrelated. Accordingly, any combination of irradiation parameterε which reεultε in formation of a cell preparation containing a plurality of cellular nucleic acid-pεoralen monoadductε and εubstantially no cellular nucleic acid-psoralen crosεlinks iε intended to be embraced by the inεtant invention. As used herein, the phrase, "substantially no crcsεlinkε", referε to a cell εuεpenεion in which greater than 50% of the pεoralen photoadductε are psoralen- onoadducts . As illustrated in the referenced Examples, substantially higher percentages of pεoralen monoadductε can be obtained by εelecting different irradiation parameters, quantitating the photoadducts formed thereby and syεtematically εelecting that combination of irradiation parameters which yields the desired psoralen-monoadduct percentage (See e.g., Examples 3 and 4), For therapeutic applications, it may be desirous to have a cell preparation containing 100% psoralen-monoadductε. In contrast to the instant invention, prior art psoralen photoactivation methods, i.e., irradiation of a cell suspension with ultraviolet A radiation in the presence of psoralen, yield a cell εuεpension containing greater than 50% pεoralen croεεlinkε. In a preferred embodiment, the cellε are leukocytes from human fluid sampleε, e.g., peripheral blood, lymph fluid, bone marrow, lymphatic organ tiεsue or cell cultures derived therefrom. Leukocytes are white blood cells which include lymphocytes (T cells and B cells), polymorphonuclear cells and monocyteε . In a preferred embodiment, the leukocytes are T cells. In accordance with the instant invention, the cells are photochemically altered and are administered to a subject to modify the subject's immune system response. It is believed that the damaged cells act as a non-specific adjuvant to augment the immune reεponεe. Although the cells contain variouε target moleculeε which may be photochemically altered by irradiation with visible light in the presence of a plurality of psoralen molecules, cellular nucleic acid serves as the principal target for psoralen photoadduct formation. In accordance with the instant invention, the psoralen molecules bond to pyrimidine baεeε in DNA to form pεoralen-DNA monoadductε. As used herein, the term psoralen refers to photoactivatable molecules containing both a furan and a pyrone ring. Psoralens are inert prior to exposure to radiation and are transiently activated to an excited εtate following irradiation. Due to the abεorption characteriεticε of pεoralenε (diεcuεεed below) , these agents historically have been activated with ultraviolet A radiation. A key aspect of the instant invention is the discovery that, despite the low extinction coefficients at visible wavelengths, visible light may be uεed to activate pεoraler. to a transient species which is capable of photochemically alkylating a target molecule, such as cellular DNA. One of the most widely used psoralens, and the only psoralen currently approved for clinical use, is 8-methoxypsoralen (8-MOP), the structure of which iε shown in figure 1. The absorption spectrum for 8-MOP (disεolved in abεolute ethanol) shows subεtantial absorption at wavelengths between about 200 nm and 320 nm, a precipitous drop in absorption at wavelengths between 320 and 400 nm (ultraviolet A) and very little absorption at wavelengths greater than 400 nm (figure 2 and Example 1). The extinction coefficients for 8-MOP at selected wavelengths (300, 350, 400, 420 and 450 nm) are included in figure 2 to illustrate the low but finite absorbance by 8-MOP in the viεible region of the εpectrum. The extinction coefficientε were derived from gravimetrically determined molar concentrations of 8-MOP. By comparing the extinction coefficients at 350 nm and 420 nm (2016 and 0.60 M respectively) one would predict that a nearly 3360-fold increase in radiation dose at 420 nm would be required to deliver the same number of absorbed photons (and hence induce a similar number of photoadducts) aε a radiation dose at 350 nm. Surprisingly, a much smaller dose of viεible radiation (20-fold) is required to form psoralen-DNA monoadducts than would be predicted based upon the extinction coefficient of 8-MOP at 419 nm (Example 2) . As discloεed in Examples 2 and 3, the unanticipated efficiency of psoralen-DNA monoadduct formation under conditions of visible light irradiation is, at least in part, due to a reduced rate of pεoralen and/or monoadduct degradation upon exposure to viεible wavelength irradiation compared to the relatively high rate of degradation of theεe compoundε upon expoεure to ultraviolet wavelength irradiation (figure 3) . Figureε 4 and 5 schematically illustrate the formation of psoralen monoadducts and crosεlinkε upon absorption of a firεt and a second photon of radiation, respectively. The term monoadducts refers to a psoralen-modified target molecule in which the active group of the target molecule is covalently coupled to either the furan ring (4',5'-MA or 4 ' ,5 '-monoadduct) or the pyrone ring (3,4-MA or 3,4-monoadduct) of psoralen. In theory, upon absorbing a first photon of light, 8-MOP covalently bonds to a pyrimidine base of DNA (figure 4) to form a psoralen-monoadduct. We believe that the monoadduct iε incapable of abεorbing a εecond photon of light at visible light wavelengths. Thus, irradiation of 8-MOP and DNA with visible light permits accumulation of psoralen-DNA monoadducts without the attendant formation of psoralen-DNA crosslinks. In contrast to the instant invention, reaction of DNA and psoralen in the presence of ultraviolet A irradiation results primarily in the formation of psoralen-nucleic acid croεslinkε (i.e., greater than 50% of all photoadductε) aε a reεult of additional photon absorption by pεoralen-DNA monoadducts (figure 5). As previously mentioned, such croεεlinkε currently are reported to be the moεt mutagenic type of psoralen-DNA lesion. Monoclonal antibodies which recognize 8-MOP-DNA photoadducts in irradiated cellε may be uεed to determine the optimum amount of viεible light irradiation to achieve optimal psoralen-DNA monoadduct formation (see Yang et al. , "8-MOP DNA Photoadductε in Patientε Treated with 8-MOP and UVA", J. Inveεt. Dermatol . 92:59-63 (1989). Gaεparro, et. al., alεo have reported methods for the quantitation of both the overall level of photoadduct formation (Gasparro, F.P., et al . , "Repair of 8-MOP photoadducts in human lymphocytes" DNA Damage and Repair in Human Tisεueε (edε. B.M. Sutherland and A.D. Woodhead) Plenum Press, NY, p. 137 (1990)) and the extent of monoadduct and crosslink formation (Bevilacqua, P.M., et al . , "High performance liquid Chromatography analysis of 8-methoxypsoralen monoadducts and crosεlinks in lymphocytes and keratinocytes" , J. Invest. Dermatol 97:151-155 (1991)). The ratio of monoadducts and crosslinks produced upon activation of psoralen in the presence of a target molecule depends, at least in part, upon the rate of monoadduct formation relative to the rate at which the monoadduct proceeds to crosεlink (Sastry, et al., supra. ) . Applicants have discovered that the distribution of photoadducts also depends upon the rate of psoralen and/or monoadduct degradation at the wavelength of irradiation. These degradation rates are proportional to the extinction coefficients of the psoralen and monoadduct at the wavelength at which the irradiation takes place. The rate of psoralen and/or monoadduct degradation has not previously been considered as a factor in determining the distribution of photoadductε in a photoreaction. Meaεurement of the relative ability of ultraviolet A (UVA) and viεible radiation to induce 8-MOP photodegradation is diεclosed in Example 2 and illustrated in figure 3. The reεultε indicate that εhorter UVA wavelengths (320 and 340 nm, for example) much more efficiently degrade 8-MOP than longer UVA wavelengths or visible light. Thus, the shorter wavelength components of UVA radiation appear to directly degrade 8-MOP, thereby reducing the effective concentration of drug available for photoreactions with DNA. The εhorter UVA wavelengthε may alεo reduce the level of photoadduct formation by inducing the photoreverεal of already formed photoadducts (Tesεman, J., "Photochemiεtry of furan-side 8-methoxypsoralenthymidine monoadduct inεide the DNA helix. Converεion to diadduct and to pyrone-εide monoadduct.", Biochem. 24:1669-1676 (1985)). Example 3 deεcribes formation and quantitation of photoadducts present in bovine aorta smooth muscle cellε following treatment with 8-methoxypεoralen (1000 ng/ml) and 2 419 nm light (up to 12 J/cm ). Cellular DNA was isolated, hydrolyzed using nucleolytic enzymes and analyzed by reverse phase HPLC aε deεcribed in the Example. The primary effect of uεing 419 nm light having an intensity of 7 J/cm 2 in lieu of long wavelength ultraviolet radiation was a more than tenfold reduction in the extent of croεslink formation (Example 3, Table 1). The irradiation conditions may be selected to provide 100% monoadducts (Example 4, Table 3). A reduction in crosεlink formation when visible light iε used for psoralen activation may also reduce the mutagenicity of 8-methoxypεoralen and hence enhance its therapeutic efficacy, e.g., by permitting photomodification of cells under non-cytotoxic conditionε to produce mutant, viable cells for administration to a patient. Various assayε are known to thoεe of εkill in the art for determining cell viability. For example, the relative proportionε of viable and non-viable cellε in a cell preparation may be determined by expoεing an aliquot of the preparation to trypan blue and comparing the number of cellε which exclude tripan blue with the number of cells which adsorb the dye. Viable cells have an intact membrane which acts to exclude trypan blue. In addition to 8-methoxypsoralen (8-MOP), preferred psoralens include 4 '-aminomethyl- 4,5' ,8-trimethylpsoralen (AMT), 5-methoxypεoralen (5-MOP) and trimethylpεoralen (TMP) . AMT iε a synthetic, water soluble analogue of 8-MOP. This and other synthetic water soluble analogues of 8-MOP are described in Berger et al . , "The Medical and Biological Effects of Light", Annalε of N.Y. Academy of Science 453 :80-90 (1985). Some inveεtigatorε have reported that 5-MOP iε not aε efficaciouε as 8-MOP in the treatment of psoriasis (Calzavara-Pinton, et al . , Exptl. Dermatol. 1:46-51(1992)). TMP is widely uεed to treat vitiligo patientε reεulting in the repigmentation of depigmented areas of skin. 8-MOP is presently the only psoralen approved for use in clinical applications. 8-MOP may be adminiεtered orally to the patient or introduced directly into the εuεpension of cells. The conditions for oral administration of 8-MOP are described in U.S. Pat. No. 5,147,289, the contents of which have been incorporated herein by reference. Following oral administration, psoralens are absorbed from the digestive tract, reaching peak levels in the blood and other tissues in one to four hours and are excreted almost entirely within 24 hours. Introduction of the psoralen molecules directly to the cell suspension offers several advantages over oral dosage administration. Dosage levels are more easily monitored and maintained jin vitro . Moreover, extracorporeally administered psoralenε can be attached to drug carrierε that would otherwise be too toxic for oral administration. Such carriers can be used to target the agent into a specific cell or into a particular cell location, e.g., the cell nucleus to target nuclear DNA. For example, insulin has been used to carry large photoreactive molecules, e.g., fluorescein and psoralen, into activated T lymphocytes and monoclonal antibodieε have been uεed to deliver lipoεomes with photoreactive pyrene incorporated into itε membrane to target T cellε (see Berger, C, et al., "Comparison of Synthetic Psoralen Derivatives and 8-MOP in the Inhibition of Lymphocyte Proliferation", Annals of N.Y. Academy of Science 453:80-90 (1985). Such carrier mediated photoactivatable drug delivery can be used in accordance with the present invention to deliver a photoactivatable drug directly to the target cell. The invention also provides a method for making a pharmaceutical preparation for administration to a mammal. The εuεpenεion of cells containing cellular nucleic acid molecules are contacted with a plurality of psoralen molecules to form a pεoralen-cell εuεpenεion. The pεoralen-cell εuεpenεion is irradiated with visible light to form a cell suεpenεion containing a plurality of cellular nucleic acid-pεoralen monoadductε and subεtantially no cellular nucleic acid-pεoralen croεεlinkε. The cell εuεpenεion may be placed in a pharmaceutically acceptable carrier at any εtage during the photomodification reaction, e.g., before or after irradiation with viεible light. The invention further provides a method for modifying the immune system response of a mammal to an antigen. In contrast to photopheresis methods of the prior art, the present invention discloεes the use of visible light radiation to photoactivate psoralen. Photopheresis procedures are described in U.S. Patent No. 5,147,289, the contents of which have been incorporated herein by reference. Photopheresiε may be performed on a continuous εtream, aε described in the Edelεon '289 patent, or may be performed batchwise. Briefly, continuouε photophereεiε, as applied to the instant invention, comprises withdrawing the leukocytes from the patient, forming the suεpenεion of cellε into an extracorporeal εtream, flowing the εtream through a treatment chamber substantially transparent to visible light radiation, irradiating the stream in the chamber with visible light radiation in the presence of the plurality of psoralen moleculeε, and administering the irradiated leukocytes to the patient. Psoralen molecules may be orally administered to the patient prior to withdrawing the cell material from the patient for treatment. Alternatively, psoralen molecules may be added extracorporeally to the cell suεpension. Photopheresiε requireε that the above-deεcribed pharmaceutical compoεition be adminiεtered to the mammal to augment the mammal ' ε immune response. In an alternative embodiment, the irradiated cells containing the nucleic acid-psoralen monoadducts are stored in aliquotε containing an amount of cells sufficient to augment the immune responεe of the mammal . Aε described above, determination of the amount of cells neceεεary to augment the patient 'ε immune reεponεe is within the ordinary skill of the art. Preferably, an amount of cells ranging from a minimum of about 25,000 to a maximum of about 200 x 10 antigen presenting cells is sufficient. The εuεpenεion of cells containing cellular nucleic acid-psoralen monoadductε iε returned to the patient according to any appropriate mode of administration known in the art, e.g., injection into the blood stream or the immune εyεtem of the patient. In the preferred embodimentε, the method for modifying the immune εyεtem reεponεe further compriεeε the εtep of artificially contacting the mammal ' ε immune system with an antigen for a εuitable period of time to stimulate the immune syεtem. Aε uεed herein, the term, "artificially εtimulate" or "artificially contact" referε to the poεitive step of contacting and stimulating the immune system of a subject with an antigen through human intervention. The subject (patient, hoεt) to be treated in the present invention is a mammal, preferably a human. The artificial contacting of the subject's immune system with the specific antigen may be achieved in any manner which introduces the antigen into the subject's immune εyεtem, e.g., by injection directly into the blood εtream, the lymphatic system, the lymphoid organs, or the skin. The antigen is then permitted to be in contact with, or exposed to, the subject 'ε immune εyεtem, for a εuitable time period εo aε to permit εtimulation of certain leukocytes specifically in responεe to that antigen. Thiε εuitable period of time could be aε long as one year but in most instances is shorter and generally is no longer than 72 hours. As used herein, the term antigen refers to any molecule capable of inducing an immune response and includes peptides, nucleoproteinε, nucleic acids, polysaccharides and analogues of these molecules. The term analogue includes the above-identified antigens which have been modified, e.g. , by chemical agents or enzymatic cleavage, εynthetic moleculeε containing all or part of the above-identified antigenε, aε well aε hybrid moleculeε, e.g., molecules containing portions of at least two different antigens. The analogues are prepared using chemical or biochemical syntheεiε methodε, e.g., by employing cloning techniques, according to methods within the ordinary skill of the art. In general, an antigen is any molecule which can potentially elicit an immune system response. Thus, the term antigen includes autologous antigens, e.g., circulating tisεue antigens associated with an autoimmune diseaεe and cancer antigenε that are preεent in autologouε cancer cellε but are not expressed in a non-neoplastic state, as well as exogenous antigens. Preferred antigens include proteins and/or peptides asεociated with an allergic reaction (e.g., poiεon ivy, penicillin), a pathological state, an immunodeficiency disease or a hypersensitivity diεeaεe. Exemplary immunodeficiency diseaseε include acquired immunodeficiency syndrome (AIDS), certain forms of cancer, immunodeficiency of old age, and immunodeficiency following immunosuppresεive therapy. Hyperεenεitivity diεeaεe iε broadly defined to include delayed-type hyperεensitivity reaction, autoimmune disease, allergy, infectious disease, rejection of allografts, and graft-versus-host reaction. More εpecifically, exemplary autoimmune diεeaεeε include rheumatoid arthritis, pemphigus vulgaris, syεtemic εcleroεiε and εyεtemic lupus erythematosuε . Exemplary AIDS-related antigenε include core protein p24, envelope protein gpl20, gp41, gp55, and gp66/31 (Biεaccia, E. et al. , εupra.). Antigenε asεociated with a pathological εtate, e.g., peptideε derived from a εolid tumor malignancy, are iεolated by surgically removing all or part of the tumor and extracting the tumor-asεociated antigenε. In addition, tisεue culture εupernatantε from suspensions of the malignant cells and plasma of patients with malignancy can serve as sources of the tumor asεociated antigens. Exemplary cancer antigens include tumor antigens such as those described by P. Boon in "Toward a Genetic Analyεiε of Tumor Rejection Antigenε", Adv. Cancer Reε. 5_8: 177-210(1992) . As discloεed in Boon, εupra. , exemplary tumor antigens include: P91A, P35B, P198 and P1A and correεponding mutants, discloεed therein. The term antigen also includes antigens associated with a hypersenεitivity diεease, and in particular, antigenε aεεociated with a hyperεenεitivity diεeaεe mediated by the clonal expansion of circulating aberrant T cellε. In a preferred embodiment, the antigen iε derived from a clonotypic T cell receptor. The preεent invention thuε provideε a method for enhancing a clone-εpecific immune reaction which killε or inhibitε proliferation of an aberrant population of T cellε. Alεo within the εcope of the invention are pharmaceutical compoεitionε for modifying an immune reεponεe to an antigen. The compoεition compriεeε a pharmacologically acceptable carrier and a preparation of cellε containing a plurality of cellular nucleic acid-pεoralen monoadducts and subεtantially no cellular nucleic acid-pεoralen croεεlinks. In a preferred embodiment, the ratio of psoralem monoadduct to croεεlinks is at least about 2 to 1, more preferably, about 10 to 1, and most preferably 49 to 1. Accordingly, the photoactivated cell suspension advantageously contains cellε having an enhanced population of non-lethal mutationε (cauεed by the abεence of pεoralen-crosslinks) in comparison with cells treated using conventional photopheresis procedures, e.g., exposure to psoralen in the presence of ultraviolet A radiation. Optionally, the pharmaceutical composition further contains a concentration of antigen which is capable of stimulating an immune response. In general, a concentration of antigen up to about 100 ug/ml is preferred although subεtantially lower antigen concentrations may be used. See e.g., Hosken, N. , et al. , "Claεε I-reεtricted presentation occurs without internalization or procesεing of exogenouε antigenic peptideε", J. Immunology 142(4) : 1079-1083 (1989) and Townεend, A., et al. , "The epitopeε of influenza nucleoprotein recognized by cytotoxic T lymphocytes can be defined with short synthetic peptideε", Cell 44 :959-968 (1986). A determination of the optimum antigen concentration for eliciting an immune reεponεe is within the level of skill of the art without undue experimentation. EXAMPLES The formation of 8-methoxypsoralen-DNA monoadductε and croεslinkε iε preεumed to be reεponsible for the efficacy of photochemotherapieε that employ 8-methoxypεoralen activated with long wavelength ultraviolet radiation (UVA, 320-400 nm) . The following examples demonstrate that 8-methoxypεoralen can alεo be activated with viεible light at 419 nm or 447 nm. Example 1. Abεorption Spectrum of 8-methoxypεoralen (8-MOP) . The abεorption spectrum of 8-MOP (Sigma, St. Louis MO) dissolved in absolute ethanol (either 0.010 or 10 mg/ml) was recorded from 200-500 nm using an LKB Ultrospec II. Extinction coefficientε, derived from the gravimetrically determined molar concentrations, are shown for the following wavelengths: 300, 350, 400, 420 and 450 nm. The concentrationε of all diluted solutions were verified either spectrophotometrically or by HPLC analysiε (deεcribed below) . The abεorption εpectrum of 8-MOP iε plotted with the extinction coefficient on a logarithmic εcale in order to illustrate the low but finite abεorbance in the viεible region (figure 2). A comparison of the extinction coefficients at 350 nm and 420 nm (2016 and 0.60 M ~ reεpectively) would predict that a nearly 3360-fold greater doεe of the latter wavelength energy would be required to deliver the εame number of abεorbed photons at 350 n and hence induce a similar number of photoadducts. In fact, a much smaller doεe of viεible radiation waε required to form photoadductε in bovine smooth muscle cells than predicted based upon the relative extinction coefficients at these wavelengths (see Examples 2 and 3). Example 2. Photodegradation of 8-MOP: Comparison of Visible and Ultraviolet A radiation. The relative ability of ultraviolet A (UVA) and viεible radiation (VIS) to induce 8-MOP photodegradation waε measured. 8-MOP (1034 ng/ml) disεolved in ethanol waε expoεed to doεes of either ultraviolet A (UVA) radiation (4.5 2 mW/cm , window glaεε filtered) or 419 nm radiation (6.5 2 mW/cm ) . The 8-MOP concentration at time zero iε indicated by daεhed line in figure 3. Aliquotε (0.25 ml) were taken at 30, 60 and 90 min. and analyzed by HPLC (Gaεparro, F.P., et al . , "Rapid and sensitive analysis of 8-methoxypsoralen in plaεma", J. Invest. Dermatol. 90:234-236 (1988)). An 2 exposure of UVA (8 J/cm ) for 30 min. led to 22% 8-MOP degradation. A comparable dose of 419 nm light led to 2.2% degradation. In other studies we have observed that shorter UVA wavelengths (320 and 340 nm, for example) were much more efficient at 8-MOP degradation than longer UVA wavelengths (J. Battista, unpublished results). Thus, the εhorter wavelength components of UVA radiation may degrade 8-MOP and may effectively reduce the concentration of drug available for photoreactions with DNA bases. In addition, the shorter UVA wavelengths may effectively reduce the level of photoadduct formation by inducing the photoreverεal of already formed photoadductε (Teεεman, J.W., et al . , "Photochemiεtry of furan-εide 8-methoxypεoralen-thymidine monoadduct inεide the DNA helix. Conversion to diadduct and to pyrone-side monoadduct", Biochem, 2_4: 1669-1676 (1985)). Example 3. Formation of Psoralen-DNA Monoadducts in Smooth Muscle Cell Using Visible light (419 nm) . (A) Bovine Aorta Smooth Muscle Cells. Thoracic aortas were removed aεeptically from calveε and smooth muscle cells (SMC) were obtained by an explant method. Briefly, the veεεelε were opened in a laminar flow hood and the endothelial cell layer waε mechanically scraped off. Two millimeter punch biopsieε of the aorta media layer were obtained and placed in a culture diεh with media conεiεting of Dulbecco' ε modified Eagle'ε Medium (DMEM, GIBCO, Grand Iεland NY) εupplemented with 10% (v/v) heat inactivated fetal calf εerum, antibiotics (300 units/ml each of penicillin and streptomycin) and 0.2 M L-glutamine (GIBCO). The smooth muscle cell biopsies were left at 37°C in a 5% CO,-, incubator until SMC explants were detected. SMC are differentiated from fibroblaεtε by their appearance during confluency, forming hill and valley morphology whereaε the latter produce a whorl type of appearance. In addition, SMC proliferation waε inhibited by heparin (0.1 mg/ml) and antibody specific for SMC actin (HHF35, Enzo Diagnoεtics, NY NY) waε used as an immunologic marker for SMC actin. SMC were sub-cultured with 0.01% trypsin/EDTA and SMC from passageε 3 to 7 were uεed. (B) Irradiation. The SMC were incubated with 8-MOP 1050 ng/ml including 0.5-1.5% [ 3 H]8-MOP (εpecific activity, 83 Ci/mmol; Amerεham, Arlington Hts IL) in Hank's Balanced Salt Solution (HBSS) for 30 min. in the dark prior to irradiation. A photochemical reactor (Southern New England Ultraviolet Co., Branford, calf thymuε) equipped with εix 8 watt lampε emitting viεible light (centered at 419 nm, +17 nm at half height) waε used to irradiate the cells at a distance of 12.5 cm (the lamps were equally spaced over a 135° angle) . An 2 . . . irradiance of 6.5 mW/cm was determined using a calibrated εilicon diode UV250Bq (EG&G, Montgomeryville PA). The spectral output of the 419 nm lampε (figure 6) waε determined by focuεing the light onto a Jarrell-Aεh Monoεpec 27 (Allied Analytical, Waltham MA) equipped with an optical spectral multichannel analyzer and a diode array detector (Princeton Instruments, Princeton NJ) . ( C) DNA Isolation . After treatment with 8-MOP and either visible light or UVA radiation, the cells were washed to remove unbound 8-MOP and any low molecular weight degradation productε. The cellε were detached from the petri diεheε by trypεinization. DNA waε iεolated aε described previously (Bevilacqua, P.M., et al. , "High performance liquid Chromatography analysiε of 8-methoxypεoralen monoadductε and croεslinks in lymphocytes and keratinocyteε" , J^ Invest. Dermatol. 9_7: 151-155 (1991)). The DNA concentration waε determined εpectrophotometrically at 260 nm after recording the full εpectrum from 200 to 400 nm (LKB UltroSpec II. Piεcataway NJ) . (D) Characterization of 8-MOP photoadduct formation. The specific activity of [ H]8-MOP was used to calculate the extent of photoadduct formation using duplicate 0.020 ml aliquots of the iεolated DNA. DNA waε hydrolyzed using nucleolytic enzymes and then analyzed by a slightly modified reversed phase HPLC protocol (Bevilacqua, P.M., et al . , "High performance liquid Chromatography analyεis of 8-methoxypsoralen monoadductε and croεεlinkε in lymphocyteε and keratinocyteε", J__ Invest. Dermatol. 97: 151-155 (1991). To each 0.5 ml faction, 4 ml of scintillation fluid (Ecoscint, National Diagnosticε, Manville NJ) waε added prior to εcintillation analysis (LKB Rack Beta). HPLC analysiε of enzymatically hydrolyzed DNA from the 419 nm/8-MOP treated SMC is shown in Fig. 7. The pattern of peaks iε comparable to that previouεly found for cellε treated with UVA and 8-MOP (Bevilacqua, P.M., et al . , "High performance liquid Chromatography analyεiε of 8-methoxypεoralen monoadductε and crosslinks in lymphocytes and keratinocyteε" , J_ Invest. Dermatol. 97:151-155 (1991). The peak eluting near fraction 25 correspondε to the crosslink (XL); the peak near fraction 50, the 3,4-MA (pyrone ring monoadduct); and those at fractions 53-62, the 4 ' , 5 '-MA (furan ring monoadduct). (E) Results. In the case of 419 nm irradiation at 7 J/cm 2, the primary photoadduct was the furan ring monoadduct (84.2% yield). The yield of pεoralen-crosslink were much lower than thoεe obtained for the cellε treated with UVA (Table 1). The reduction in croεεlink formation iε a reεult of the relative change in extinction coefficientε for 8-MOP and 4 ' ,5 '-MA beyond 380-390 nm, i.e., the monoadduct iε apparently incapable of abεorbing a εecond photon of light at the viεible wavelengthε to generate the pεoralen croεεlink. 2 The treatment of SMC with 1050 ng/ml 8-MOP and 7 J/cm 419 nm radiation led to the formation of 9.7 adducts/ megabaεepair (mbp) of DNA. At a higher 419 nm intenεity (12 2 J/cm ) , a proportionately greater number of photoadductε were formed (the average of two runε waε 14.4 adducts; see Table 1). UVA irradiation of the cells at an intenεity of 2 2 J/cm led to the formation of 88 photoadduct/mbp. The linear relation between adduct formation and the product of 8-MOP and UVA doεeε would predict the formation of 308 adductε/mbp 5 uεi•ng 7 J/cm2. Thuε, although the ratio of extinction coefficientε for the UVA and viεible wavelengthε was 3360 the ratio of photoadducts fell within a factor of 20 (at 7 J/cm 2 ) . TABLE 1 Adduct Distribution in Cells Treated with 8-MOP Irradiation Wavelength adducts/mbp Percentage Photoadduct 4 ' ,5'- 3,4,- crosε- MA MA link 7 J/cm 2 419nm 9.7 84.2 13.3 2.5 12 J/cm 2 419nm 15.3 85.6 7.8 6.4 (run 1) 12 J/cm 2 419nm 13.5 77.3 11.9 10.8 (run 2) 2 J/cm 2 UVA 88.0 40.9 11.7 47.4 Example 4. Formation of Pεoralen-DNA Monoadductε in Solution: Modification of Calf Thymuε DNA with 8-MOP and Viεible Light (419 nm and 447 nm) . (A) Materials; Nuclease P, (EC 3.1.30.1) from Penicillium citrinum, deoxyribonuclease I (DNase I; EC 3.1.21.1) from bovine pancreaε, and alkaline phoεphatase (EC 3.1.3.1) type VII-S from bovine intestinal mucosa in suεpension (2-4 U/ul) and calf thymuε DNA (highly polymerized) (all from Sigma, St. Louiε, MO) were uεed without further purification. Other materialε included: [ HJ-8MOP (79 Ci/mmol, Amerεham, Arlington Heightε, IL) , 8-MOP (Aldrich, Milwaukee, WI), triethylamine (Fluka, Ronkonkoma, NY) acetic acid (Fiεher Scientific, Pittεburgh, PA), Ecoεcint scintillation fluid (Ecoεcint, National Diagnoεticε, Manville, NJ) , HPLC grade water and HPLC grade methanol (MeOH) (J.T. Baker, Inc., Phillipεburg, NJ), and 0.25% Trypsin-EDTA (ethylenediaminetetraacetic acid), Dulbecco'ε Phosphate Buffered Saline (DPBS), Hank's Balanced Salt Solution (HBSS) (without phenol red), and fetal bovine serum (Gibco BRL, Betheεda, MD) . Other chemicals were reagent grade and uεed without further purification. (B) DNA Hydrolysiε The procedure uεed for DNA hydrolysis was adapted from a procedure reported by Singhal, et al. , "High-performance liquid chromatography for trace analysis of DNA and kinetics of DNA modification," BioChrom. 4:78-88 (1989). A stock solution containing 1 U/ul Nuclease P and 0.1 U/ul DNase I in water and a 10 mM ZnCl 2 and 30 uM NaOAc pH 5.3 buffer solution were prepared. The amount of DNA in each sample was determined by measuring the optical density (OD) at 260 nm using an Ultraspec II (Pharmacia LKB) . For each OD of DNA in the sample (5 OD maximum, 200 ul maximum volume), one ul of the enzyme stock and 10 ul of the buffer were added (two and twenty ul minimum, respectively) , and the sample waε incubated at 37°C for 2 hours. Thereafter, 10 ul of 1 M sodium glycinate, pH 8, and 1 ul of alkaline phosphataεe were added per OD of DNA (twenty and two ul minimum, reεpectively) , and the εample waε incubated at 37°C for 3 hourε. After centrifugation to remove any εuεpended εolids, the sampleε were directly injected onto the HPLC column for analyεiε. (C) HPLC Analysiε A Regiε Rexchrom ODS (octyldecylεilyl) column (4.6 x 250 mm, 5 micron, Regiε, Morton Grove, IL) was used in conjunction with a Spectra-Physics (San Jose, CA) SP8800 ternary HPLC equipped with a Spectra-Focuε forward optical εcanning detector (200-360 nm) and Spectra Focuε Software package for detection and integration. Injectionε were made uεing a Rheodyne 7125 injection port and eluting fractions were collected (Frac-100, Pharmacia LKB, Piscataway, NJ) at 0.5 min intervals (flow rate = ϊ ml/miri) into scintillation vials (Simport, American Bioanalytical, Natick, MA). Scintillation analysis was performed by adding 4 ml scintillation fluid to each fraction and counting on a Beta counter (60 εecond count, RacBeta, Pharmacia LKB). The relative percent of each component detected waε determined by summing the counts aεεociated with that component (minuε background) and dividing by the total countε . The eluentε and gradientε uεed are liεted in Table 2. 8-MOP photoadductε in εplit doεe εtudieε TABLE 2 HPLC MOBILE PHASE GRADIENT CONDITIONS eluent A: MeOH flow rate: 1.0 ml/min eluent B: 0.1 M triethylammonium acetate pH 6.8 fraction size: 0.5 min gradient: time(min) 0.0 0.1 3.5 16.0 23.0 33.0 36.0 38.7 41.0 %A 5.5 9.0 15.7 25.5 25.5 32.5 32.5 35.5 100.0 %B 94.5 91.0 84.3 74.5 74.5 67.5 67.5 64.5 0.0 (D) Photoadduct Formation in Calf Thymuε DNA Solutionε of Calf thymus DNA (10 OD/ml, 1.54 mM) , 8-MOP (180 uM) and [ 3 H]8-MOP (1 ul/100 ul) were prepared in 10 mM Tris, 1 mM EDTA and 0.1 M NaCl, pH 7.8, and three 5 ul aliquotε removed for εcintillation analyεiε for εpecific activity measurements. A 300 ul aliquot was irradiated at 419 nm (with a 17 nm bandwidth) for 1.0 or 4.0 hours at 4°C using a fluorescent lamp emitting at 419 nm. Irradiations were also performed on 300 ul aliquots at 447 nm (20 nm bandpaεε) for 1.0 or 4.0 hourε. The spectral output of the 419 nm (figure 6) and 447 nm (figure 8) lamps waε determined by focusing the light onto a Jarrell-Ash Monoεpec 27 (Allied Analytical, Waltham, MA) equipped with an optical εpectral multichannel analyzer and a diode array detector (Princeton Inεtru entε, Princeton, NJ) . The εampleε were precipitated and waεhed twice, aε deεcribed above, and then rediεεolved to their original volume with HPLC water. Aliquotε were removed for ultraviolet εpectroεcopic and εcintillation analyεeε to determine binding levelε (aε above), and 20 ul aliquotε from each sample were removed and digested for HPLC analysis. 3 Solutions of 1.54 mM Calf thymuε DNA, [ H]8-MOP, and either 50, 100 or 200 uM 8-MOP were prepared in the standard buffer for concentration studies, with aliquotε removed from each sample for scintillation analyεiε to determine εpecific activity. The εampleε were precipitated and washed twice, then analyzed as above. Irradiation of calf thymus-DNA (1.54 mM) and [ 3 H]-8-MOP (180 uM) with 419 nm led to the formation of 1.28 (1 hour) and 4.48 (4 hourε) adductε/kilobase, with the adducts detected by digestion and HPLC analysiε (See Table 3, this Example). The distribution of adducts at 1 hour waε: 0% croεεlink; 5.8% 3,4-monoadduct and 94.2% 4 ',5'-monoadduct. At 4 hourε irradiation at 419 nm, the diεtribution of adductε waε: 6.4% crosslink; 9.7% 3,4-monoadduct; and 83.9% 4 ' ,5'-monoadduct. Irradiation of calf-thymus-DNA aε above, but with 447 nm light, led to the formation of 0.109 (1 hour) and 0.446 (4 hourε) adductε/kilobase. The distribution of adducts at 1 hour was: 0% croεεlinkε, 0% 3,4-monoadducts and 100% 4 ' 5 '-monoadductε. At 4 hourε irradiation at 447 nm, the distribution of adducts was: 1.7% croεεlinkε; 7.5% 3,4-monoadductε; and 90.8% 4 ',5 '-monoadducts . Aε expected, the major photoadduct formed waε the furan-ring monoadduct (4 ' ,5 '-monoadduct) . Irradiation of the calf thymuε-DNA and [ H]-8-M0P at two different visible wavelengths led to the formation primarily of monoadducts with a small percentage of crosεlinkε, as determined by digestion and HPLC analysiε. In abεolute termε, the extent of adduct formation, aε well aε the amount of each adduct, increaεed steadily with increasing irradiation. The increase in monoadduct formation at 447 nm and one hour irradiation indicates not only that visible light can be used to activate pεoralen but that a combination of irradiation parameterε may be εelected to obtain the moεt deεired distribution of photoadducts in the treated cell suεpenεion. TABLE 3 Distribution of Photoadducts Following 419 and 447 nm treatment of DNA with 8-MOP adducts/kb Croεε 3,4 mono- 4 ',5' mono- link adduct adduct 419 nm 1 hour 1.28 0 5.8 94.2 4 hour 4.48 6.4 9.7 83.9 447 nm 1 hour 0.109 0 0 100 4 hour 0.446 1.7 7.5 90.8 Lamp output: 419 nm 6.4 mW/cm 2 447 nm 5.6 mW/cm Note: Uεing UVA roughly 50% of the adductε would be croεslinks (XL) . It εhould be underεtood that the preceding iε merely a detailed description of certain preferred embodiments. It therefore should be apparent to thoεe εkilled in the art that various modifications and equivalents can be made without departing from the spirit or scope of the invention. What is claimed iε:

Claims: CLAIMS 1. A method for forming a εuεpenεion of leukocyte cellε containing cellular nucleic acid-pεoralen monoadductε, the method compriεing the εtepε of: (a) contacting the εuspenεion of leukocyte cells containing cellular nucleic acid molecules with a plurality of psoralen molecules to form a psoralen-cell suεpenεion; and (b) extracorporeally irradiating the pεoralen-cell εuspension with viεible light to form a plurality of cellular nucleic acid-psoralen photoadducts including monoadducts and crosslinks, wherein the ratio of the monoadducts to crosεlinkε iε at leaεt about 10 to 1. 2. A method as claimed in claim 1, wherein the psoralen-cell suspenεion iε irradiated with viεible light to form the suspenεion of cellε, wherein the ratio of the monoadductε to croεεlinkε iε at leaεt about 49 to 1. 3. A method as claimed in claim 1, wherein the leukocyte cells are T cells. 4. A method as claimed in claim 1, wherein the psoralen is selected from the group conεiεting of 8-methoxypεoralen, aminomethyltrimethylpsoralen, 5-methoxypsoralen and trimethylpεoralen. 5. A method for making a pharmaceutical preparation for adminiεtration to a mammal, compriεing the εtepε of: (a) contacting a suspenεion of leukocyte cellε containing cellular nucleic acid moleculeε with a plurality of psoralen molecules to form a psoralen-cell suspension; (b) extracorporeally irradiating the psoralen-cell suεpenεion with viεible light to form a plurality of cellular nucleic acid-pεoralen photoadductε including monoadductε and crosεlinkε, wherein the ratio of the monoadductε to crosslinks is at leaεt about 10 to 1; and (c) placing the irradiated pεoralen-cell εuεpenεion in a pharmaceutically acceptable carrier. 6. A method as claimed in claim 5, wherein the pεoralen-cell εuεpenεion iε irradiated with viεible light to form the εuεpenεion of cellε, wherein the ratio of the monoadducts to crosεlinkε is at least about 49 to 1. 7. A method for modifying the immune system responεe of a mammal to an antigen, compriεing the εtepε of: (a) contacting a εuspension of leukocyte cellε containing cellular nucleic acid moleculeε with a plurality of pεoralen moleculeε to form a pεoralen-cell εuεpenεion; (b) extracorporeally irradiating the pεoralen-cell εuεpenεion with viεible light to form a plurality of cellular nucleic acid-pεoralen photoadductε including monoadductε and croεslinks, wherein the ratio of the monoadducts to crosslinks is at leaεt about 10 to 1; (c) placing the irradiated pεoralen-cell suspension in a pharmaceutically acceptable carrier to form a pharmaceutical preparation for modifying the immune reεponεe; and (d) adminiεtering the pharmaceutical preparation to the mammal . 8. A method aε claimed in claim 7, wherein the pεoralen-cell εuεpenεion iε irradiated with visible light to form the suεpenεion of cellε, wherein the ratio of the monoadducts to crosεlinkε iε at leaεt about 49 to 1. 9. A method aε claimed in claim 7, wherein the cellε are T cells. 10. A method as claimed in claim 7, wherein the psoralen is selected from the group consiεting of 8-methoxypεoralen, aminomethyltrimethylpεoralen, 5-methoxypsoralen and trimethylpsoralen. 11. A method aε claimed in claim 7, further comprising the step of storing the pharmaceutical preparation prior to adminiεtration. 12. A method aε claimed in claim 7, further compriεing the εtep of: (e) artificially contacting the mammal's immune εyεtem with the antigen for a εuitable period of time to εtimulate the immune εystem. 13. A method as claimed in claim 12, wherein the psoralen-cell suspension is irradiated with viεible light to form the suspenεion of cellε, wherein the ratio of the monoadducts to crosslinkε iε at least about 49 to 1. 14. A method as claimed in claim 12, wherein the cells are T cellε. 15. A method aε claimed in claim 12, wherein the pεoralen iε εelected from the group consisting of 8-methoxypsor len, aminomethyltrimethylpεoralen, 5-methoxypεoralen and trimethylpεoralen. 16. A method aε claimed in claim 12, wherein the antigen iε εelected from the group conεiεting of an autologouε antigen, an antigen associated with a solid tumor malignancy, an antigen asεociated with an immunodeficiency diεeaεe, an antigen associated with a hypersenεitivity diεease, and an antigen asεociated with an autoimmune diεeaεe. 17. A method as claimed in claim 16, wherein the antigen is an autologous antigen. 18. A method aε claimed in claim 16, wherein the antigen is associated with an autoimmune diseaεe. 19. A pharmaceutical compoεition for modifying an immune εystem responεe to an antigen, comprising: a preparation of leukocyte cells, the cells containing a plurality of cellular nucleic acid-psoralen photoadducts including monoadducts and crosslinks, wherein the ratio of the monoadducts to crosεlinkε iε at least about 10 to 1; and a pharmaceutically acceptable carrier. 20. A pharmaceutical composition as claimed in claim 19, wherein the ratio of cellular nucleic acid-psoralen monoadducts to nucleic acid-psoralen crosεlinkε iε at leaεt about 49 to 1.

Inventors: EDELSON RICHARD L, GASPARRO FRANCIS P, EDELSON, RICHARD, L., GASPARRO, FRANCIS, P.
Applicants: UNIV YALE, YALE UNIVERSITY
Application year: 1994
Main classification: A61K35
IPC codes: A61K35, A61K39, A61K41